Danakil Depression, Ethiopia

Sam has a thing for intensely hostile environments. Phil doesn't. For the first time ever we decided to split up, with Sam joining an extraordinary expedition into the badlands of the Afar. Phil read his book.

The jaunt into the world's most vicious desert required a fully kitted-out Land Rover convoy. Armed guards riding atop the jeep were not necessarily comforting, but the threat from rogue nomads was very real.

In this eerie landscape the ground is of jagged basalt and the fumes from bubbling sulphur bleach clothing. A few people brave the environmental extremes to cut salt and load this valuable resource onto camel trains that cross hundreds of miles to be sold for $5 a slab.

The climax of this geologist's dream field trip is to peek over the edge of a volcano's crater and into a cauldron of magma. Erta Ale is one of only a few flowing lava lakes in the world.

Salt Caravan (video clip)

Tablets of salt are strapped to recalcitrant camels before plodding out through the desert.

Rock-Hewn Churches of Tigrai, Ethiopia

Dotted around the north of the country are dozens of monastic retreats carved into inaccessible cliff faces. Getting to see a few of them required effort and a head for heights.

Enclaved in these remote spots, deep in Africa, Christianity took on some astonishing twists. We were thrilled to see this fresco of Jesus, the Virgin Mary and the archangels - all with black faces.

Holy men arrived here in the 5th century after fleeing persecution in what is now Syria. They brought with them their belief in the Bible and their habit of living as hermits.

Following in their footsteps, we edged along horrible cliff footholds and into the very rock itself to discover breathtaking religious artworks and relics.

We sought rational answers to explain the amazing engineering in these improbable places. But facts and myths are so interwoven here that we learned to just shrug and go along with imaginative explanations such as "angels built this".

Addis Ababa, Ethiopia

Our first port of call in Addis was to see the 3.2 million year old Lucy. The first walking ape is a fascinating evolutionary find. But the impish 8 year olds made us giggle an awful lot more.

Ethiopia's food is fantastically tasty. We feasted on spicy mezzes of veggie treats served on the sour flatbread injera.

Axum, Ethiopia

We battled our way by local bus for another history lesson. Axum was the capital of one of the greatest empires the world has ever seen. Yet no-one seems to know anything about it, except for a clutch of myths and these enigmatic stelae.

These imperial tombstones saw their pomp between 400BC and 100AD, when the Axumites controlled a vast trading network link from Rome to ancient India. Pride came before a fall when the grandest obelisk, at 33 metres, crashed to the ground.

It now points the way to the Church of Our Lady Mary of Zion. The place where, if you so believe, the actual Ark of the Covenant now resides. Quite a history lesson.